Horology: time measuring systems or devices – Power supply details – Electrical
Patent
1997-11-03
1999-03-09
Nguyen, Matthew
Horology: time measuring systems or devices
Power supply details
Electrical
G04B 100
Patent
active
058810285
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a power supply unit for an electronic timepiece, and, especially to a power supply unit for an electronic timepiece using a mechanical generator as a power generating section.
DESCRIPTION OF THE BACKGROUND ART
In the past, an electronic timepiece which is operated by electric energy converted from mechanical energy generated by the rotation of an eccentric weight was developed and produced commercially. Also, a power supply unit used for an electronic timepiece is proposed, for example, in Japanese Patent Publication (KOKOKU) No. 52229/1995.
FIG. 3 is a view of a circuit block diagram of a power supply unit for a conventional electronic timepiece.
In FIG. 3, a power generating section 1 comprises a rotating means 11 composed of an eccentric weight or the like, an accelerating oscillating wheel 12 for accelerating the rotation of the rotating means 11, a rotor 13, a generating coil 14 which generates an AC current corresponding to the rotation of the rotor 13, and the like. A diode 2 rectifies the AC current generated by the generating coil 4 and prevents the reversal of the flow of current from a battery section 3 illustrated below.
Also, a voltage detecting section 4 outputs a signal when the potential of the battery section 3 exceeds a prescribed value. An overcharging preventive section 5 is operated by the signal from the voltage detecting section 4 to prevent overcharge exceeding the withstand voltage of the battery section 3. In this case, the battery section 3, which is composed of a condenser with a large capacity, accumulates the electric power generated by the generating coil 14 and outputs this electric power to a timepiece circuit 6.
In the power supply unit of this conventional electronic timepiece, when the rotating means 11 such as an eccentric weight or the like installed in a wrist timepiece is rotated corresponding to the hand shaking action of the user, the rotation is accelerated by the accelerating wheel 12 and transferred to the rotor 13. The rotor 13 is composed of a permanent magnet, which is rotated to generate an AC current in the generating coil 14. This AC current is rectified by the diode 2 and accumulated in the large-capacity condenser 3 used as an power storing section. This accumulated power allows the timepiece circuit 6 to operate, thus driving the electronic timepiece.
Then, sufficient electric power is stored in the large capacity condenser 3. When the electric power exceeds the prescribed voltage (for example, 2.5 V), the voltage detecting section 4 outputs a detection signal at an "L" level to operate the overcharging preventive section 5 composed of a PMOS transistor. In this manner, the AC current generated in the power generating section 1 is discharged from the overcharging preventive section 5 so that it is not accumulated in the large capacity condenser 3.
Therefore, the potential of the large-capacity condenser 3 never exceeds the prescribed value and hence the breakdown of the condenser 3 caused by high voltage is prevented. Here, the overcharging preventive section 5 is disposed closer to the battery section 3 than the position of the diode 2 to avoid the breakdown caused by high voltage when the diode 2 generates a reverse current. Generally, the maximum AC current generated by the generating coil 14 is in the order of tens of mA. Therefore, in order for the overcharging preventive section 5 to function sufficiently, the resistance of the overcharging preventive section 5 in operation is required to be in the order of tens of ohms in the case where the withstanding voltage of the large capacity condenser 3 is in the order of 2.5 V.
A titanium-lithium ion secondary battery with a large capacity (hereinafter called "secondary battery") has recently been utilized as the battery section instead of the large-capacity condenser. However, because the internal resistance of this titanium-lithium ion secondary battery is as large as tens to hundreds of ohms, the potential of the secondary battery exceeds the prescr
REFERENCES:
patent: 4441825 (1984-04-01), Morokawa
patent: 5001685 (1991-03-01), Hayakawa
patent: 5701278 (1997-12-01), Higuchi et al.
Fujita Kenji
Higuchi Haruhiko
Citizen Watch Co. Ltd.
Nguyen Matthew
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